Survey identifies drugs most likely to be found in the environment
provided by American Chemical Society
team of Johns Hopkins researchers says antidepressants, anticonvulsants, anticancer drugs and antimicrobials are the types of pharmaceuticals most likely to be found at toxicologically significant levels in the environment. Their conclusions are based on a survey of the 200 most sold and prescribed drugs in the United States.
Padma Venkatraman, PhD, one of the study's lead authors, presented estimates of probable environmental concentrations (PECs) of the top 200 drugs to scientists gathered here for the 223rd national meeting of the American Chemical Society, the world's largest scientific society.
We're trying to make an intelligent guess as to what's out there in the environment and what's probably toxic, Venkatraman said during an interview. As for any danger to people, We certainly don't have any evidence that most pharmaceuticals pose a human health risk, although the presence of carcinogens or teratogens even at low concentrations is of potential human health concern, she emphasized.
Any danger from the drug concentrations is more likely to be to aquatic organisms than humans, according to Venkatraman. Our research suggests that certain existing drugs may be present at levels at which they have the potential to exert sublethal effects.
The survey is based on calculated total drug sales and prescriptions and a search of the medical literature, said Venkatraman. Based on the existing data about the drug's biochemistry and existing data on its metabolism, we came up with the estimates.
Because some drugs are not metabolized before elimination, the researchers calculated PECs with and without metabolism, Venkatraman noted. Also, there is the fact that expired medications are often flushed down the toilet, she added. Although the survey focused primarily on prescription drugs, some over-the-counter drugs, such as ibuprofen, were included, Venkatraman said. Although Venkatraman would not specifically name the top individual drugs that are likely to be found at significant concentrations, she did highlight the classes of compounds that we think might be important.
Antimicrobials, anticonvulsants and anticancer drugs are among the classes of compounds that the researchers suspect may be found at the highest concentrations, according to Venkatraman.
Measuring environmental contaminants is target-specific, Venkatraman noted. The aim of the research is to help other scientists better target their searches for pharmaceutical compounds of environmental importance, she said. We're hoping we'll be able to give them a basis to guess what's likely to be persistent and what's likely to be used in great quantities and therefore likely to be out there in the environment also.
Research into the fate of pharmaceuticals in the environment got a kick-start in this country from similar studies done in Europe several years ago. But there are differences between those studies and the Johns Hopkins study, said Venkatraman. For instance, there was a Danish study that looked at the top 20 [drugs sold and prescribed in Denmark]. If you compare our study to theirs, only about one-third, or less, of the drugs that show up in their top 20 even show up in our top 200. There's not much of an overlap.
Differences in prescription practices, climate, and drinking water and sewage treatment account for the disparity between the studies, according to Venkatraman. As an example, she noted: Many US cities employ sewage treatment that's more rudimentary than what you'd see in most European cities. Ozone, which is more reactive than chlorine, is widely used as a disinfectant in Europe, while we use chlorine. In Europe, the use of activated charcoal to remove trace organics in drinking water treatment is also much more prevalent than in our country.
The Johns Hopkins study complements the results of the first nationwide study of drugs in the nation's streams, according to the researchers. That study, done by the US Geological Survey was published last month in Environmental Science and Technology, one of the American Chemical Society's leading peer-reviewed journals.
One area of the research that Venkatraman says she is very excited about is the use of innovative analytical techniques to measure drug concentrations in the environment. As an example, she noted, We are modifying existing derivatization techniques to adapt them to our analytes of interest. Derivatization basically involves chemical modification of compounds in order to make them more amenable to analyses by gas chromatograph.
Padma Venkatraman, PhD, is a postdoctoral fellow in the Department of Geography and Environmental Engineering at Johns Hopkins University in Baltimore, MD.